We do not in fact have any definite evidence of Gelion's ultimate outflow, but it seems unavoidable that its waters would have reached the Great Sea eventually.

Tolkien himself seems rather uncertain about the river's name. The earliest translation is into Old English (from volume IV of the History of Middle-earth) as Glæden, making it an equivalent of the later Gladden River. At another point (The Etymologies in volume V) he also associated it with Elvish roots meaning 'merry' and 'bright'. In late notes, he seems to have intended to adjust the name to make its ultimate source Dwarvish: Gabilán, meaning simply 'great river'.